BO's are the ones with the reputation to be low on the pecking order and prone to being bullied, and this has been my experience, though I haven't had a lot of either; had about 4 or 5 BO's at one point. The one I have left has been hanging around in a nest a lot, or else chasing roos to get mated (!) and she's the only one I have with raggedy looking feathers on her back, whether from the mating or being pecked or both. She's certainly not high in the pecking order and generally avoids the flock; I never see her getting pecked. I'd say isolate for a week then reintroduce, if you only had one or two BO's. My mixed flock has worked things out peacefully, and I read on here that they usually do, but still, the breeds tend to stay together. I suspect you're right that things could just get worse there, if you add more BO's; I'd think the old ones would teach the new ones their ways. Not much of an answer, but this gives you a bump.

I have half BO and half EE. They were raised together from day old chicks and they get along great. They've never known any different, so that may be why. I do notice that 3 BOs that went to fair together seem to have their own little club, but other than that they mingle nicely with no pecking of anyone. I had a couple roosters, which were a pain in the arse, but since they were butchered, it's all peacefull in the coop.